ABSTRACT
The effects of acid activation of Laponite RD (Lap) on the structure and properties of activated Lap nanoparticles (aLap) and the properties of polyNIPAAm hydrogels physically cross-linked by aLap have been studied. The acid activation of Lap by the sulfuric acid was done using the concentration of sulfuric acid within the interval Ca = 0.525-14.58% for 10 h. For slightly activated samples (Ca ≤ 1.25 wt %), the significant increase of the specific surface area (by ≈1.56 times) was accompanied with a significant decrease in both the values of the specific heat of immersion in water and n-decane. However, the hydrophilic properties of all samples S0-S5 were still observed. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) data, Fourier transform infrared (FTIR) spectra, and X-ray diffraction (XRD) patterns demonstrated that the acid activation resulted in the destruction of the crystal lattice of Lap, leaching of magnesium and lithium, and formation of the amorphous phases. Moreover, the acid activation significantly affected aggregation and negative surface charges of the aLap faces in aqueous suspension. The effects of aLap on the swelling properties and cooperativity in the phase transitions of polyNIPAAm hydrogels cross-linked by aLap are also discussed. It was demonstrated that an increase in Ca resulted in a significant increase in the equilibrium degree of swelling of the hydrogels and a decrease in the hydrogel phase-transition temperature from the swollen phase to the shrunken phase.
ABSTRACT
In this work, a new material for in vitro plant rooting based on highly dispersed polyacrylamide hydrogel (PAAG) enriched with amber powder was synthesized and investigated. PAAG was synthesized by homophase radical polymerization with ground amber addition. Fourier transform infrared spectroscopy (FTIR) and rheological studies were used to characterize the materials. They showed that the synthesized hydrogels have physicochemical and rheological parameters similar to those of the standard agar media. The acute toxicity of PAAG-amber was estimated based on the influence of washing water on the viability of plant seeds (pea and chickpea) and Daphnia magna. It proved its biosafety after four washes. The impact on plant rooting was studied using the propagation of Cannabis sativa on synthesized PAAG-amber and compared with agar. The developed substrate stimulated the rooting of the plants to more than 98% in comparison to standard agar medium (95%). Additionally, the use of PAAG-amber hydrogel markedly enhanced metric indicators of seedlings: root length increased by 28%, stem length-by 26.7%, root weight-by 167%, stem weight-by 67%, root and stem length-by 27%, root and stem weight-by 50%. This means that the developed hydrogel significantly accelerates reproduction and allows obtaining a larger amount of plant material within a shorter period of time than the standard agar substrate.